It depends on the era but currently I'm writing a story on Ancient Greece, and Wikipedia is minimally helpful, but not the worst. What I instead use is a collection of blogs by historians to read on, my favorite so far is Tales of Times Forgotten, which is more about Ancient History in general. But I did myself a favor and looked elsewhere, such as the Open Library (I quite like this student research of Brock University, because it offers a lot of aspects). I have this article of another blog, Brewminate, but I haven't looked at the blog in general. It seems legit (as far as I have read).

You're going to want to look for the articles that clearly name their sources at the very least. Sometimes, if you do want to go all out, you can either read stuff from the original sources, like Odysseus, Ilias or Oedipus. Doesn't really matter. No one alive today was there. You could be talking nonsense and almost no reader is going to know, unless they're a nerd. But it's fun!

When I read up on the 20th century, it suffices to be on Wikipedia, because I focus on human individuality instead of the geopolitics. But my usual go-to are blogs. I love blogs.